prokaryotes - bacteria see Domain Bacteria Woese et al. 1990
   Domain "Bacteria" Woese et al. 1990
     Phylum "Firmicutes" corrig. Gibbons and Murray 1978 (Approved Lists 1980)
       Class Clostridia Rainey 2010
         1 Order Clostridiales Prévot 1953 (Approved Lists 1980)
         2 Order Halanaerobiales corrig. Rainey and Zhilina 1995
         3 Order Natranaerobiales Mesbah et al. 2007 [monotypic]
         4 Order Thermoanaerobacterales Wiegel 2010